Understanding NATO's Article 5 and Collective Defence (nato.int)

• Article 5 obliges each Ally to assist, but does not specify the type or degree of assistance.
• It has been invoked only once, in response to the 9/11 attacks on the United States.
• NATO has enhanced deterrence on its eastern flank since 2014.

"Article 5 of the North Atlantic Treaty is NATO's core principle: an armed attack on one member is considered an attack on all. This article explains its history, legal basis (UN Charter), trigger mechanisms, and the sole invocation after the 9/11 attacks. It highlights deterrence through joint defence capabilities and adaptation to new threats like cyber and hybrid warfare."